Soil husbandry specialist, Steve Townsend turns his myth-busting attention to residue management in the latest in our series. – “You should incorporate your crop residues”
Over the years since they stopped us burning our stubbles an inordinate amount of time and effort – not to mention horsepower, diesel and machinery cost – have been put into straw incorporation.
More efficient combine straw choppers and spreaders and better disc and tine cultivators have really helped in the move away from ploughing. So, once again, we’ve got all those rough old stubbles neatly buried away to give us tidy seedbeds we can be proud of. At the same time, we’ve reinvested a valuable source of carbon in our soil organic matter bank. What’s not to like?
Well, in my experience, just about everything. Mainly because, more often than not, crop residues in the seedbed create problems for the establishment of our next crop physically, chemically and biologically.
As well as interfering with sowing depth by hair-pinning, they physically get in the way of seed-to-soil contact and make effective consolidation more challenging. As if this wasn’t enough, their breakdown chemically hoovers-up available soil nitrogen and phosphate which tend to be in short supply anyway at drilling time, especially in the autumn and with reduced tillage. And biologically, the range of organic acids produced by their breakdown can seriously affect seed germination and rooting where the residues are in close contact with the establishing crop.
Bury them securely below the seed germination zone and crop residues will cause you far fewer problems in all these respects. But this demands the sort of time-consuming full inversion ploughing seldom seen these days.
Equally, and particularly with heavy ground, it often means incorporation with so little air that straw breakdown is restricted and largely anaerobic. Which builds-up a layer of root-inhibiting toxins and, in many cases too, an oxidation pan.
So how can we make the most of the valuable organic matter in our crop residues without opening ourselves up to these problems? The answer – as it so often seems to be in nature – is simple; and involves altogether less horsepower, time, diesel and machinery cost. It does, however, require patience and a fresh attitude to seedbed preparation.
Providing they have enough moisture, it’s a fact that straw and chaff decay much better in the open air than ever they do underground. So all we have to do is chop our residues, spread them evenly and leave them on the surface for nature to do its thing.
Here their breakdown can be surprisingly rapid and we take advantage of a willing army of earthworms, beetles and other invertebrates to do the incorporation for us. Here too, our crop residues will act as a very effective first assault on weeds; physically suppressing them and biologically restricting their germination and development – just as they do when buried with crop seed in the ground.
Like a good garden mulch, residues on the surface can also be invaluable in restricting soil moisture loss and in protecting vulnerable soils from surface damage from heavy rainfall; particularly where the ground is left uncropped for more than a few weeks.
All very well, I hear you say, but we can’t leave our straw on the surface and get a ‘decent’ seedbed. True, with this approach we have to do without nice, tidy, pub-proud seedbeds with the wall-to-wall tilth that are a Suffolk-coulter driller’s dream. But we have the perfect way of getting just the tilth we need around the seed where it actually matters while leaving the rest of the ground where it is. It’s called direct drilling.
Evenly and consistent
The best of today’s cultivator and no-till drills are adept at drilling evenly and consistently through residues. Not only that but by moving the least amount of soil they wake-up the least amount of black-grass, brome and other troublesome weeds. And they have the least possible effect on the active biology that gives us the most resilient soils.
As ever, the devil is in the detail. Paying enough attention to straw chopping and spreading as we combine is, for instance, crucial; so crucial that we need to treat it with as much care and attention we would our first cultivation – which it effectively is. The key here is a consistent, even spread across the surface.
A timely dose of glyphosate ahead of drilling is likely to pay dividends in taking out weeds like black-grass and sterile brome which germinate particularly well out of direct sunlight under a surface mulch.
The final thing we need to appreciate about this very much better approach to residue management is that it only delivers its full benefits as part of a well-planned move into no tillage that allows the natural soil structuring processes to reassert themselves from depth; a move which takes time and should never be rushed.
The right approach here we have found will very effectively deal with both the slugs and autumn wetness which can cause difficulties with cereal straws left on top of heavy ground.
Between exploring more of what he sees as today’s most damaging soil management myths with us, Steve Townsend is more than happy to discuss any tillage or soil management issues, interests or concerns with Farmers Guide readers by e-mail on [email protected] or by phone on 01452 862696.